Apparatus for actuating tooling

ABSTRACT

Riveting apparatus wherein a planetary roller screw delivers the high forces required for actuating the fastener upset tooling. In order that precise control of the entire upset operation me by obtained, a servo-controlled electric motor operates the actuator. In order that different machining operations may be performed on a workpiece without having to provide an actuator for each tool, the tools are engaged in turn by the actuator for performing riveting and other machining in succession.

[0001] The present invention relates generally to the actuation ofriveting and other tooling in the art of automatic fastening. Thepresent invention also relates to automatic fastening apparatusincluding riveting apparatus.

[0002] Conventionally, riveting apparatus for airplane fuselages or wingpanels and the like has been hydraulically-operated. An example of suchhydraulic riveting apparatus is found in U.S. Pat. No. 5,060,362 toBirke et al, which is assigned to the assignee of the present inventionand which is hereby incorporated herein by reference. However, othertypes of riveting apparatus such as pneumatic, electromagnetic, androller screw have been suggested.

[0003] Pneumatic driven riveting apparatus, while typically small andhand-held, is very noisy and inefficient and difficult if not impossibleto place under electronic control due to the compressibility of air.

[0004] The standard riveting apparatus for many years has beenhydraulic. While hydraulic riveting apparatus has been considered quiteeffective and reliable, providing high linear forces for installingrivets, slugs and similar fasteners in workpieces, it has also beenconsidered desirable that riveting apparatus be provided which isquieter, faster, and more repeatable while still having theeffectiveness and reliability of hydraulic riveting apparatus.

[0005] U.S. Pat. No. 1,483,919 to Walker suggests a riveting machinewhich utilizes an electrically operated screw which rotates with therotating element of the riveting motor, utilizing separate means forholding the screw against rotation during a riveting stroke andreturning the screw to the starting point at the end of the rivetingstroke. Walker also discusses a construction in which the screw isnon-rotatable, the rotating element of the motor constituting a nutwhich is rotatable but held against movement in the axial direction.This actuating apparatus may not be able to generate the high forceswhich may be required for some riveting operations. Other art which maybe of interest includes U.S. Pat. Nos. 434,677; 2,075,162; 2,342,089;and 5,404,633.

[0006] U.S. Pat. No. 5,491,372 and published International applicationno. PCT/US94/10232 (WO 95/08860) to Erhart, which, along with U.S.patent application Ser. No. 08/154,953 on which the Internationalapplication claims priority, are hereby incorporated herein byreference, disclose an electrically powered linear actuator including anactuator assembly having an actuator rod and a thread engaging portion,a motor assembly having a stator, and a housing. The thread engagingportion of the actuator assembly is moved along the threaded extent of acylinder on rotation thereof which cylinder functions as an armaturedrive cylinder. The stator is selectively energized to rotate thearmature drive cylinder clockwise or counterclockwise to reciprocallymove the thread engaging portion of the actuator assembly and an outputshaft of the actuator. A closed-loop feedback control includes aservo-amplifier, controller, and master controller for the actuator.

[0007] Such a roller screw actuator, identified as a GS series invertedroller screw actuator, is marketed by Exlar Corporation of Chanhassen,Minn. for applications such as automated assembly, ball screwreplacement, dispensers, hydraulic cylinder replacement, machine tools,pneumatic cylinder replacement, pressing, stamping, indexing stages,material cutting, precision grinders, automatic tool changers, chip andwafer handling, die cutters, formers, material handling, parts,clamping, etc. Another commercially available actuator, identified byExlar as an FT series roller screw force tube actuator, utilizes aroller screw mounted inside a periscoping tube mechanism. Othercompanies such as GSA-Gewinde Satelliten Antriebe AG of Horriwil,Switzerland, INA Bearing Company, Inc. of Fort Mill, S.C., and SKFTransrol of France also provide planetary roller screws.

[0008] Riveting apparatus must be rugged and be able to apply the hugeforces required for fastener upset on such workpieces as aircraftfuselages and wing panels. Thus, as previously mentioned rivetingapparatus for many years has been principally hydraulic. If anon-hydraulic riveting apparatus is to become practical, it must be ableto ruggedly and reliably apply such high fastener upset forces.

[0009] It is accordingly an object of the present invention to providenon-hydraulic riveting apparatus which is rugged and reliable, is ableto apply the high fastener upset forces which are required, and hassufficient speed of operation, efficiency and durability.

[0010] It is another object of the present invention to provide suchriveting apparatus which is quiet, safe, is easily maintained, has longlife, and has quick turn-around time for repairs, yet is inexpensive andmay be operated inexpensively.

[0011] It is considered desirable that the riveting apparatus becontrollable throughout the entire fastener upset operation so that theapparatus may be applied to different fastener alloys and so thatrepeatability and uniformity rivet-to-rivet may be achieved.

[0012] It is therefore a further object of the present invention toprovide non-hydraulic riveting apparatus which is controllablethroughout the entire fastener upset operation.

[0013] It is yet another object of the present invention to successivelyperform different machining operations on a workpiece without having toprovide such a riveting apparatus actuator for each tool.

[0014] In order to provide quiet, safe, effective, easily and quicklyrepairable, inexpensive, and reliable non-hydraulic riveting apparatuswhich can deliver the high upset forces, in accordance with the presentinvention, a planetary roller screw is provided for actuating thefastener upset tooling.

[0015] In order that precise control of the entire fastener upsetoperation may be obtained, in accordance with the present invention, aservo-controlled electric motor is provided for operating a screw orforce tube actuator for a fastener upset tool.

[0016] In order that different machining operations may be performed ona workpiece without having to provide an actuator for each tool, inaccordance with the present invention, the tools are engaged in turn bythe actuator for performing riveting and other machining in succession.

[0017] The above and other objects, features, and advantages of thepresent invention will be apparent in the following detailed descriptionof the preferred embodiment of the present invention when read inconjunction with the accompanying drawings wherein the same referencenumerals denote the same or similar parts throughout the several views.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0018]FIG. 1 is a diagrammatic perspective view of one form of rivetingapparatus which embodies the present invention.

[0019]FIG. 2 is a sectional view taken along the axial length of analternative embodiment of an actuator for the riveting apparatus of FIG.1.

[0020]FIG. 3 is a front view of an actuator in accordance with anotheralternative embodiment of the present invention.

[0021]FIG. 4 is a side view, partly in section, thereof.

[0022]FIG. 5 is a top view thereof.

[0023]FIG. 6 is a side view of the actuator of FIGS. 3, 4, and 5attached to a riveting tool and mounted to one type of a machine frame,shown partially and in section.

[0024]FIG. 7 is a front view similar to that of FIG. 6 of the actuator,riveting tool, and machining frame thereof.

[0025]FIG. 8 is an enlarged view of the portion of FIG. 6 showingattachment of the actuator to the riveting tool.

[0026]FIG. 9 is a side elevation view of another type of machine framewith the actuator of FIGS. 3, 4 and 5, a riveter, and other machiningtools mounted thereto.

[0027]FIG. 10 is a view thereof taken along lines 10-10 of FIG. 9.

[0028]FIG. 11 is an enlarged view of a portion of the apparatus as shownin FIG. 9, showing detachable attachment of the actuator to a machinetool.

[0029]FIG. 12 is a view thereof taken along lines 12-12 of FIG. 11.

[0030]FIG. 13 is a functional block diagram illustrating servo-controlof an actuator in accordance with the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0031] In the automatic fastening apparatus according to the presentinvention, the fastener upset tool as well as other tools in theapparatus, is actuated by a roller screw operated by a suitablycontrolled motor, the roller screw preferably being a planetary rollerscrew and the motor preferably being a servo-controlled electric motor.The roller screw actuator can be of various types, for example onewherein an external controlled motor causes a nut to rotate and effectlinear movement of a screw shaft for driving the fastener upset tool.Alternatively, the motor armature may serve as the nut which advancesalong a screw which is stationary linearly, the nut causing movement ofa force tube attached at one end to the nut and having the fastenerupset tool on the other end thereof. In another form, the screw shaft isrotated by the motor causing linear movement of the nut which in turncauses linear movement of a force tube attached to the nut for drivingthe fastener upset tool. The automatic fastening apparatus of thepresent invention is used for installing various types of fasteners inworkpieces including, but not limited to, rivets, slugs, bolts and pins.

[0032] Referring now to FIG. 1, there is illustrated generally at 20 oneform of the apparatus of the present invention including an electric ramcomprising a threaded screw or shaft 22 and a nut 24 which threadedlyengages the screw 22 to provide a ball or roller screw. The nut 24 hasan enlarged circular lower portion 26 which is suitably mounted forrotation on a supporting structure 28 and has gear teeth 30 around theperiphery thereof. The screw 22 passes through a hole (not shown) in thesupporting structure 28. A motor 32 is suitably mounted to thesupporting structure 28, and its shaft is provided with a gear 34 whichengages gear 30 for rotating the nut 24 which in turn effects linearmovement of the screw 22. An upper linear guide 36 comprises an elongatefirst member 38 which is rigidly attached to the supporting structure 28and extends parallel to the screw 22. A second member 40 is dove-tailedwith or otherwise suitably attached to member 38 for movement along thelength thereof and is suitably threadedly connected to screw 22 forlinear movement in response to rotation of the nut 24 in order tomaintain an accurate screw position in a plane perpendicular to thelongitudinal axis of the screw. A lower linear guide 42 comprises firstand second members 44 and 46 respectively which are similar to first andsecond members 38 and 40 respectively.

[0033] The screw 22 is shown to carry or is otherwise suitably alignedto a suitable turntable/clamp cylinder 48 and a lower rivet upsettingtool or anvil 50, and linear movement of the screw 22 effects actuationthereof with enough force to upset a fastener such as a rivet or slug.As is conventionally known in the art, force is also applied to theopposite end of the fastener by another tool (not shown) for suchfastener upset. This tool as well as the tooling 48 and 50 isconventional in the art and will therefore not be described further. Forexamples of riveting tooling and apparatus for positioning thereof, seeU.S. Pat. No. 5,477,597, which is assigned to the assignee of thepresent invention and which is incorporated herein by reference, as wellas the previously discussed U.S. Pat. No. 5,060,362.

[0034] As compared to a ball screw, wear of a roller screw is equalizedover a greater contact area so that a roller screw riveter may be ableto undergo an order of magnitude greater number of operating cyclesbefore maintenance is required. This translates into longer life, andless energy use is required for operation than would be required for anequally powerful hydraulic riveter.

[0035] In order that the linear movement of the screw 22 be controllablethroughout the rivet upset operation so that repeatability anduniformity rivet-to-rivet may be achieved and print-outs thereofoptionally provided to the customer as well as allow application todifferent fastener alloys, the motor 32 is servo-controlled, i.e. motor32 is connected to motion controller 506 and servo-amplifier 507 forcontrol of the operation thereof, in accordance with principles wellknown to those skilled in the art to which this invention pertains. Suchservo-control will be described in greater detail hereinafter withreference to FIG. 13. Thus, either the force or the upset distance to beapplied may be precisely computer-controlled while the other ismonitored to provide feedback as well as to optionally provide aprint-out to the customers of the fastener upset process.

[0036] Referring to FIG. 2, there is shown an alternative embodiment ofan actuator 60 for fastener upset tooling, such as the riveting tooling48 and 50 shown on FIG. 1. The actuator assembly 60 includes a threadedoutput shaft 62, a plurality of transmission rollers 64, and an electricmotor assembly including a stator 66 and a housing 70. The motorassembly moves the output shaft 62 between a retracted position, as seenin FIG. 2, and an extended position (not shown) and includes anelongated cylinder 68 formed of a magnetic material rotatably supportedrelative to the housing assembly 70. Magnets 72 are mounted about anouter surface of the cylinder 68 to form an armature (with the cylinder68) within the motor assembly. The stator 66 is attached to andsupported by the housing assembly and encircles the cylinder. Anexternal control 74 selectively energizes the stator to rotate thearmature clockwise or counterclockwise. A plurality of transmissionrollers 64 are assembled in a spaced planetary arrangement around theshaft 62 (mounted for rotation about the shaft 62) and between the shaft62 and the cylinder 68 to convert rotary motion of the cylinder 68 tolinear movement of the shaft 62. Thus, the elongated cylinder 68includes a central threaded bore 76 the threads of which are engaged bythe transmission rollers 64. The output shaft 62 has annular rings forcoupling with the transmission rollers 64 to move along the threadedbore 76 on rotation of the cylinder 68. Thus, the elongated cylinder 68forms a drive cylinder within the actuator assembly as well as formingthe armature of the motor assembly. This roller screw actuator 60 isdescribed more fully in the aforesaid Erhart patent. A suitable externalanti-rotation device (not shown) should be provided in accordance withprinciples commonly known to those of ordinary skill in the art to whichthis invention pertains, to prevent rotation of shaft 62 relative tohousing 70. Suitable anti-rotation devices should also be provided forthe other actuators described herein. Like the motor 32, the motorassembly for the actuator 60 is servo-controlled, as will be describedin greater detail hereinafter with reference to FIG. 13.

[0037] Riveting operations may require forces on the order of 50,000lbs. or more for riveting aircraft fuselages and wing panels and thelike. While the actuator 60 may be suitable for riveting operationsrequiring smaller forces, such huge forces may not be suitablyobtainable with the actuator 60 shown in FIG. 2 because the motorassembly therefor, being constrained within the housing 70, may not bepowerful enough. Referring to FIGS. 3, 4, and 5, in order to generatethe forces which may be required for riveting, there is provided analternative actuator 80 for riveting apparatus 48 and 50 which has ahousing 82 from which extends an output force tube 84.

[0038] In this embodiment, a shaft or screw 86 is suitably rotatablymounted within housing 82 such as by ball bearing assembly 88. A rollerscrew nut 90 is suitably mounted with rollers (not shown) in a planetaryarrangement around the shaft 86 and between the shaft 86 and the nut 90,similarly as illustrated in FIG. 2, for converting rotary movement ofthe shaft 86 to linear movement of the nut 90. The force tube 84 issuitably attached to the nut 90 such as by a suitable bracket 92 wherebyadvancement or retraction of the nut 90 advances or retracts the forcetube 84. The output end of the force tube 84 is suitably received in abearing 94 which is suitably mounted in the end of the housing 82 andextends through an aperture 98 in the adjacent face plate 96. The shaft86 is telescopingly and supportively received within force tube 84. Apair of guide rollers 102 (one shown) on opposite sides respectively areprovided to prevent the nut 90 and force tube 84 from rotating. Theforce tube 84 supports a follower member 100 which is suitably attachedthereto for engaging fastener upset tooling, such as that designated 48and 50 in FIG. 1. The extended position of the force tube 84 andfollower 100 for actuating a machining tool is illustrated in phantomlines. Apertures illustrated at 104 are provided for mounting theactuator to a frame, as discussed in greater detail hereinafter. As usedin the claims, a “nut” is meant to include any force tube and followerassembled therewith for linear movement.

[0039] A servo-controlled motor 106, which may be a brushless A.C. motoror other suitable motor, is provided for imparting rotary motion to theshaft 86. It is provided outside of and in the present illustrationalongside (parallel to) housing 82 so that it may be large enough togenerate the huge forces which may be required for some rivetingoperations. Alternatively, motor 106 could extend in an oppositedirection from that shown in FIG. 4, and it could also be locatedoutside of but in axial alignment with housing 82. Thus, the motor 106is outside the roller screw housing 82, and its housing 108 is separatefrom housing 82. The motor 106 is suitably coupled to a gear box 110which may, for example, provide a 3:1 planetary gear reduction for highefficiency. Sheaves 112 and 114 are suitably attached to the gear boxoutput shaft 116 and actuator shaft 86 respectively and coupled by agear belt 118 or by other suitable means. The gear belt 118 is desirablyenclosed in a protective guard member 120. For precise positioning andoperation throughout a machining cycle, the motor 106 isservo-controlled by means of servo amplifier 507 served by computer 506,as described in greater detail hereinafter with reference to FIG. 13.

[0040] As previously discussed, an actuator such as illustrated in FIG.2 is commercially available as the GS series inverted roller screwactuator previously referenced, and an actuator such as illustrated inFIGS. 3, 4, and 5 is commercially available as the FT series rollerscrew force tube actuator previously referenced. However, other suitableactuators marketed by other companies, such as those previouslyidentified, may be incorporated in automatic fastening apparatus forriveting and the like which comes within the scope of the presentinvention.

[0041] Referring to FIGS. 6, 7 and 8, there is shown at 130 one type offrame structure in which the roller screw actuator 80 is suitablymounted. The actuator 80 extends through an opening 132 in the framestructure 130. Its face plate or flange 96 shown in FIG. 8 is receivedin a pocket 136 and attached to an adaptor plate 138 by screws 137 shownin FIG. 7. Adaptor plate 138, in turn, is received in a pocket 140 inthe frame structure and attached by screws 139. The frame structure 130is provided for positioning the riveting anvil 50, as more fullydescribed in the aforesaid U.S. Pat. No. 5,477,597. An adapter fitting142 or other suitable structure is provided for attaching the actuator80 to the fastener upsetting assembly 48 and 50. The fitting 142 isattached to the follower 100 by screws 144 or other suitable means andto a plate 143 of the assembly for fastener upset by screws 146 or othersuitable means. However, it should be understood that the actuator 80may not be attached to the fastener upsetting assembly but may insteadbe positioned in butting alignment therewith, and such an embodiment ismeant to come within the scope of this invention.

[0042] Referring to FIGS. 9 to 12, there is shown actuator 80 as well asvarious tools described hereinafter suitably mounted to another type offrame structure 170 for movement toward and away from the workpiece 172,which is clampingly held in position for machining by pressure footassembly 173, within larger box structure 174. Box structure 174 is inturn suitably mounted to a curved frame 176 for movement along theworkpiece curvature, as more fully discussed in the aforesaid U.S. Pat.No. 5,477,597. Movement of box structure 170 is effected by travel motor178, which is suitably attached to box structure 174 and which effectstravel of box structure 170 carrying the riveting apparatus toward andaway from the workplace 172, using principles well known to skilled inthe art to which this invention pertains. The opposite walls of boxstructure 170 are guided by means of linear bearings 179.

[0043] The tools for effecting a riveting operation (including theinstallation of two-piece fasteners and swage collars) in the workpiece172 may include a drill 180, a hole probe 182, a shave tool 184, a sealtool 186, and a riveter or buck 188, all of which are conventional. Whenthe box or frame structures 170 and 174 have been positioned for ariveting operation, the tools are transferred successively intoposition, as hereinafter described, for carrying out their respectiveoperations so that only a single actuator is required therefor. For suchtransfer, the tools are all suitably mounted on a pair of parallel rails190 for movement therealong. As shown in FIGS. 11 and 12, one portion192 of each rail is suitably mounted, such as by bracket 194 and screws196, to the plate 143 for linear movement therewith toward and away fromthe workpiece 172 when the actuator 80 effects extension and retractionrespectively of the force tube and follower 100. Rail portions 198 onopposite sides of each rail portion 192 are suitably fixedly attached toa frame member 200 of box structure 170. The actuator 80 is suitablypositioned so that rail portion 192 is aligned with rail portions 198when the force tube 84 is retracted so as to provide one continuous railover which the tools may travel, the tools being provided with members202 which are adapted to engage the rails 190 such as in dove-tailfashion for riding therealong, in accordance with principles well knownto those skilled in the art to which this invention pertains. Rails 190,including portions 192 and 198 thereof, can be of the type of linearguides commercially available from NSK of Tokyo, Japan.

[0044] The tools are also suitably mounted to a transfer plate 204 whichis attached to a bracket 206 which is in turn mounted on ball screw 208.One end of the ball screw 208 is connected to the shaft of transfermotor 210 for rotation thereof to effect movement of the tools asdesired along the rail 190, and the other end of the ball screw 208 ismounted in a bearing 212 on the opposite side of the box structure 170,all in accordance with principles well known to those skilled in the artto which this invention pertains.

[0045] Since the actuator motor 106 is servo-controlled and is thuscontrollable by a computer program which may specify a differentoperating speed of the actuator 80 for each of the tools, in accordancewith the present invention, a single actuator 80 can thus be providedfor operation of all of the tools 180, 182, 184, 186, and 188. It shouldbe understood that the actuator may not be needed for some of the toolswhere precise positioning control is not required. If desired, theactuator force tube 84 and tools may alternatively be arranged so thatthe force tube 84 does not connect to but instead butts against ends ofthe tools, which would allow the screw to retract quickly and the toolto return to position more slowly. The tools may be spring biased toreturn to position.

[0046] As discussed in the aforesaid Erhart international application,it will be appreciated by those skilled in the art that an objective ofthe automatic fastening apparatus of the present invention, whichincorporates the servo-controlled or closed-loop feedback controlledlinear actuator, is to precisely apply linear motion to the riveting andother tools. The motion is generally programmed or defined in a computerprogram developed by the user of the actuator. For example, prior tousing the actuator, the user enters the instructions and motion profilesinto a programmable motion controller. The motion controller, whencommanded, executes the user's program by signaling a servo amplifier toapply a voltage across the actuator's stator leads. The level of voltageapplied is a function of the velocity specified in the user's programfor the specific motion being executed. The voltage causes current toflow in the stator windings of the actuator which, in turn, applies atorque to the motor armature. In the actuator assembly, the subsequentrotation of the armature is converted mechanically within the actuatorto a linear motion reflected on the actuator's output shaft.

[0047] Specific instructions for both instantaneous position andvelocity are transmitted by the motion controller for each motion to beexecuted. In response, the amplifier applies a voltage level whichrepresents an expected velocity output of the actuator. The expectedvoltage/velocity relationship is established by the user during setupand calibration of the system. It will be appreciated that for a numberof reasons, the actual velocity of the output shaft seldom exactlymatches what is being commanded by the motion controller. Thus, thearmature shaft must be monitored to assure that the actuator producesthe exact motion desired.

[0048] Referring to FIG. 13, in the present invention, this isaccomplished firstly by incorporating a velocity as derived fromposition feedback sensor 510 within the actuator assembly 80 andsecondly by designing the servo amplifier 507 and the controller 506such that continuous adjustments are made to the voltage applied inresponse to any sensed error in position and/or velocity. By doing so,continual adjustment of the system command is accomplished such that themotion produced is exactly as intended by the user. For example, if theactuator's output during a particular moment is 0.100 in. behind thetarget position at that moment and/or it is moving too slow relative tothe instructions in the user program, then the voltage will be increasedslightly to increase its speed (i.e., the controller 506 attempts toeliminate the gap between the target and actual values). This process ofchecking feedback and continuously correcting the command is commonlycalled closed-loop control.

[0049] As used in the claims, the term “servo-controlled” is intended tomean computerized control of the operation of a motor, which may utilizea predetermined program, and feedback of a condition or conditions of anactuator being driven by the motor.

[0050] In order to utilize closed-loop control, the controller 506 mustreceive information as to the position of the actuator's output shaft atall times. A previous method of deriving this information was to utilizea linear position sensor. Such sensors exist in many forms and includepotentiometers, LVDTs, or magneto-strictive types. While the accuracy ofthe feedback sensor may vary without affecting control, the velocityfeedback must be continuous and linear with respect to the voltageapplied in order for the system to operate correctly. Likewise, therelationship between the armature's movement and the sensed positionmust be continuous and linear for the closed-loop system to operatecorrectly. However, in any screw style rotary-to-linear conversionmechanism, a small amount of backlash exists, introducing error in thesesystems.

[0051] Backlash results from the fact that no mechanism can bemanufactured where all the components mesh or fit perfectly (i.e.,tolerances are near or are zero). Even if the components could fitperfectly and even assuming minimal wear, backlash would evolve. In thepresent case, it will be appreciated that backlash causes anon-linearity or discontinuity in the above described relationships atthat point where the torque being applied to the armature changesdirection. Any discontinuity in these relationships will confuse thecontroller to the extent that instability or oscillation will occur.Therefore, the point at which the greatest precision and higheststability is normally desired is also exactly the point whereinstability will most likely occur. More specifically, the motorservo-controller must accurately hold the desired output shaft positionby applying forward or reverse movement or force in response to anysensed movement from the desired position. However, due to thetolerances that backlash creates, there is a discontinuity between theapplication of forward and reverse movement. As a result, the controllercauses the linear actuator to hunt, or oscillate, back and forth in anattempt to maintain it in a final target position.

[0052] One approach to solving this problem is to eliminate backlash.This might be done by splitting one or more of the roller screwcomponents in half and then preloading the pieces against each other byan adjustable spring mechanism. If this approach is utilized, it will beappreciated that the spring tension must then exceed the actuator's loadcapacity. However, such an approach is expensive and takes up additionalspace. Further, only half of the screw mechanism carries the load. Whilethis approach may be made to work, the additional friction resultingfrom the high forces applied may substantially reduce the system'sefficiency—thereby increasing its power consumption thus reducing thelife of the unit correspondingly.

[0053] Turning to the automatic fastening apparatus of the presentinvention, since the position and velocity of the actuator output shaftis a known fixed ratio of the rotation of the armature, the preferredsolution is to measure its rotational position and velocity and allowthe motion controller 506 to calculate the resulting position of theactuator's output shaft. While backlash will allow some back and forthmovement of the output shaft, when the armature is held in position, nodiscontinuity between the voltage applied to the armature and feedbackwill occur. Therefore, in the preferred embodiment, the feedback sensor510 is mounted directly and rigidly to the armature so that stableoperation may result. Using this method, the amount of backlash mustonly be less than the system accuracy requirements of the application(i.e., the inaccuracy allowed must be greater than the total backlash ofthe converting mechanism).

[0054] A rotary position/velocity sensor may, for example, be used forthe feedback sensor 510, as illustrated in FIG. 13. Advantagesassociated with use of such a rotary feedback compared to a linearsensor device are that it is generally less expensive; it is morerugged; it does not require expensive boring of the output shaft; itmounts conveniently at the rear end of the armature; and it will be usedto derive commutation signals required for brushless motors.Alternatively, employing a linear sensor would require the use of aseparate motor commutation sensor.

[0055] It will be appreciated that the feedback loop normally includessome form of a proportional, integral, derivative control processequation. However, those skilled in the art will appreciate that othercontrol equations, such as proportional, proportional-derivative, fuzzylogic, etc. and other types of control devices may also be used. For amore detailed discussion, reference may be had to Dorf, Modern ControlSystems, pages 379 et. seq. (1981). Control equation constants for thepreferred embodiment of the present system control may be derivedempirically and may be changed depending upon the desired application.Additionally, those skilled in the art will appreciate that theconstants may also be derived by determination of the transfer functionfrom the steady-state response or other such methods as are well knownin the art.

[0056] By using the servo-amplifier 507 and controller 506, the linearpositioning of the actuator output shaft may be properly and quicklymaintained for predetermined target locations. As seen in FIG. 13,closed-loop feedback control is established by the angular positioncontrol of the rotary sensor 510 which is provided to the controller 506via line 512. The controller 506 operates in accordance with itsprogrammed position control profile and other programming steps andprovides signals to the servo amplifier 507 via line 509. In turn, theservo amplifier 507 provides the required voltage to the stator of thelinear actuator 80 via line 513.

[0057] The rotary sensor 510 may, for example, be an optical digitalencoder manufactured by Renco Corporation of California, under modeldesignation RHS25D. Such devices generally operate by utilizing a lightemitting device and a disk having a plurality of alternating opticallytransparent and opaque areas defined about the periphery. Thus, as thearmature rotates, the light is alternately blocked and allowed to passthrough the disk. A light sensitive device receives the light andprovides a signal indicative of the light intensity received by thelight sensitive device. It will be appreciated, however, that a lightemitting device and a light receiving device together form an opticalsensor, and that analog generators may also be utilized as part of theclosed-loop feedback control loop. For another example, the rotarysensor 510 may be a resolver which converts rotary motion to position.It should of course be understood that the present invention is notlimited to any particular type of rotary sensor.

[0058] As discussed hereinbefore, the actuator for riveting apparatus inaccordance with the present invention may be of various types. Forexample, the actuator may be one wherein an external motor causes a nutto rotate and effect linear movement to a shaft. Alternatively, themotor armature may serve as the nut and effect linear movement of theshaft, as in FIG. 2. For yet another example, the shaft may be caused torotate and effect linear movement of a nut to which a force tube isattached, as in FIGS. 3, 4, and 5. Automatic fastening apparatusincluding each of these types of actuators is meant to come within thescope of the present invention, and the present invention is not limitedthereto.

[0059] The automatic fastening apparatus of the present invention can beutilized in apparatus wherein the tooling is moved along and about aplurality of axes, such as in a five axis riveter of the type disclosedin the U.S. Pat. No. 4,864,702 issued Sep. 12, 1989, the disclosure ofwhich is hereby incorporated by reference. Such apparatus would be foroperation on a workpiece having opposite sides and supported on asupporting surface, such as the floor of a factory, with the sidesdisposed substantially perpendicular to the supporting surface. Theapparatus would include a frame adapted to move along the supportingsurface and along the workpiece, and carriage means movably mounted onthe frame. Positioning means would be carried by the carriage means, andriveting tools on first and second head means would be in spaced apartrelation on the positioning means, so that the tools would be located onopposite sides of the workpiece and movable toward and away from theworkpiece. The carriage means could include a pair of carriages onopposite sides of the workpiece, or a single carriage with anarrangement thereon to enable the positioning means to locate the firstand second head means on opposite sides of the workpiece. Typically, anactuator of the type shown in FIGS. 3-12 would be provided in each ofthe first and second head means for actuating the tools thereof.However,-it is within the scope of the present invention to provide theactuator of the type shown in FIG. 2 or in FIGS. 3-12 on one of the headmeans and an hydraulic or other form of actuator on the other headmeans. If desired, the first and second head means may be held by firstand second C-frames respectively wherein the workpiece is moved betweenthe head means for positioning thereof at various positions formachining, and one of the C-frames is rotated about an axis along whichthe head means are located to provide clearance for the workpiece in thevarious positions thereof for machining. Alternatively, the workpiecemay be held in a fixed position and a C-frame moved relative thereto.

[0060] The frame of the foregoing apparatus would be movable by suitablemeans in a first direction along the supporting surface and along theworkpiece. Means would be provided to move the carriage means in adirection substantially perpendicular to the first direction and towardand away from the supporting surface. The riveting tools would be movedtoward and away from the workpiece by the actuator as described above.To accommodate curvature in the workpiece, the apparatus would includemeans operatively associated with the positioning means for moving thefirst and second head means about an axis substantially parallel to thefirst direction and to the supporting surface. Also to accommodatecurvature in the workpiece, the apparatus would include meansoperatively associated with the positioning means for moving the firstand second head means about an axis substantially perpendicular to thefirst direction and to the supporting surface.

[0061] The method of the present invention can be utilized in rivetingmethods and apparatus (for slugs, two-piece fasteners, and the like) ofthe type disclosed in U.S. Pat. No. 4,908,928 issued Mar. 20, 1990 andU.S. Pat. No. 5,060,362 issued Oct. 29, 1991, the disclosures of both ofwhich are hereby incorporated by reference. In both methods the actuatorshown in FIGS. 3-12 can be employed to move either or both of the upperand lower riveting rams.

[0062] It should be understood that, while the invention has beendescribed in detail herein, the invention can be embodied otherwisewithout departing from the principles thereof, and such otherembodiments are meant to come within the scope of the present inventionas defined by the appended claims.

What is claimed is:
 1. Riveting apparatus comprising tooling means forupsetting fasteners, a shaft, a nut, means for converting rotary motionof one of said shaft and said nut to linear movement of the other ofsaid shaft and said nut for actuating said tooling means for upsettingfasteners, said converting means comprising a plurality of rollersassembled between said shaft and said nut in a planetary arrangementaround said shaft, and motor means for rotating said one of said shaftand said nut.
 2. Riveting apparatus according to claim 1 wherein saidmotor means comprises a servo-controlled electric motor.
 3. Rivetingapparatus according to claim 1 further comprising means for engagingsaid other of said nut and said shaft to a plurality of tools foractuation thereof in turn for performing riveting and other machining insuccession.
 4. Riveting apparatus according to claim 3 wherein saidengaging means comprises means for moving said tools in turn intoalignment with said other of said nut and said shaft.
 5. Rivetingapparatus according to claim 1 wherein said motor means includes ashaft, and the apparatus further comprises means for coupling said motormeans shaft to said one of said shaft and said nut.
 6. Rivetingapparatus according to claim 5 further comprising a first housing forsaid nut and a second housing for said motor means.
 7. Rivetingapparatus comprising tooling means for upsetting fasteners, a shaft, anut, means for converting rotary motion of one of said shaft and saidnut to linear movement of the other of said shaft and said nut foractuating said tooling means for upsetting fasteners, andservo-controlled electric motor means for effecting rotary motion ofsaid one of said shaft and said nut.
 8. Riveting apparatus according toclaim 7 further comprising means for engaging said other of said nut andsaid shaft to a plurality of tools for actuation thereof in turn forperforming riveting and other machining in succession.
 9. Rivetingapparatus according to claim 8 wherein said engaging means comprisesmeans for moving said tools in turn into alignment with said other ofsaid nut and said shaft.
 10. Riveting apparatus according to claim 7wherein said motor means includes a shaft, and the apparatus furthercomprises means for coupling said motor means shaft to said one of saidshaft and said nut.
 11. Riveting apparatus according to claim 10 furthercomprising a first housing in which is contained said nut and a secondhousing for said motor means.
 12. Machining apparatus comprising atleast two tools, a shaft, a nut, means for converting rotary motion ofone of said shaft and said nut to linear movement of the other of saidshaft and said nut for actuating said tools, a motor means for effectingrotary movement of said one of said shaft and said nut, and means forengaging said tools by said other of said shaft and said nut in turn forperforming machining by said tools in succession.
 13. Machiningapparatus according to claim 12 wherein said converting means comprisesa plurality of rollers engaged between said shaft and said nut in aplanetary arrangement around said shaft.
 14. Machining apparatusaccording to claim 12 wherein said motor means comprises aservo-controlled electric motor.
 15. Machining apparatus according toclaim 12 wherein one of said tools is a riveting tool.
 16. Machiningapparatus according to claim 12 wherein said engaging means comprisesmeans for moving said tools in turn into alignment with said other ofsaid nut and said shaft.
 17. Machining apparatus according to claim 12wherein said motor means includes a shaft, and the apparatus furthercomprises means for coupling said motor means shaft to said one of saidshaft and said nut.
 18. Machining apparatus according to claim 17further comprising a first housing in which is contained said nut and asecond housing for said motor means.
 19. Machining apparatus accordingto claim 12 wherein said engaging means comprises at least one rail forreceiving said tools for movement therealong, said rail having a segmentattached to said other of said shaft and said nut and at least one othersegment to which said a rail segment is alignable to move said tools insuccession on and off said a rail segment.
 20. A method of rivetingcomprising inserting a fastener in position for riveting, positioningtooling for upsetting the fastener, providing a planetary arrangement ofrollers around a shaft and engaged between a nut and the shaft forconverting rotary motion of one of the nut and shaft to linear motion ofthe other of the nut and shaft, rotating said one of the nut and shaftto thereby effect linear movement of the other of said nut and shaft tothereby actuate said tooling to upset the fastener.
 21. A methodaccording to claim 20 further comprising servo-controlling the rotationof said one of the nut and shaft.
 22. A method of riveting comprisinginserting a fastener in position for riveting, positioning tooling forupsetting the fastener, coupling an electric motor to one of a nut and ashaft for rotating thereof, converting the rotation of said one of thenut and the shaft to linear motion of the other of the nut and the shaftto thereby actuate the tooling for upsetting the fastener, andservo-controlling the motor.
 23. A method of machining comprisingproviding at least two tools, rotating one of a nut and shaft, aligningthe tools in succession with the other of the nut and the shaft,converting the rotational movement of said one of the nut and shaft tolinear movement of the other of the nut and shaft to actuate the alignedtool for performing machining.
 24. A method according to claim 23wherein the rotational movement converting step comprises providing aplanetary arrangement of rollers around the shaft and engaged betweenthe nut and the shaft.
 25. A method according to claim 23 furthercomprising servo-controlling the rotation of said one of the nut andshaft.
 26. A method according to claim 23 wherein the step of aligningthe tools comprising moving the tools in succession along at least onerail and onto a rail segment which is attached to the other of the nutand shaft.
 27. Riveting apparatus according to claim 1 or claim 7 , foroperation on a workpiece having opposite sides and supported on asupporting surface with said sides disposed substantially perpendicularto said supporting surface, said riveting apparatus comprising: a) framemeans adapted to move along said supporting surface and extending alongsaid workpiece; b) carriage means movably mounted on said frame means;c) positioning means carried by said carriage means; d) riveting toolson first and second head means in spaced apart relation on saidpositioning means, said tools being located on opposite sides of saidworkpiece and moveable toward and away from said workpiece; e) means formoving said frame in a first direction along said supporting surface andalong said workpiece; f) means for moving said carriage means in adirection substantially perpendicular to said first direction and towardand away from said supporting surface; and g) means including saidconverting means for moving said riveting tools toward and away fromsaid workpiece.
 28. Riveting apparatus according to claim 1 or claim 7 ,for operation on a workpiece having opposite sides and supported on asupporting surface with said sides disposed substantially perpendicularto said supporting surface, said riveting apparatus comprising: a) framemeans adapted to move along said supporting surface and extending alongsaid workpiece; b) carriage mean movably mounted on said frame means; c)positioning means carried by said carriage means; d) riveting tools onfirst and second head means in spaced apart relation on said positioningmeans, said tools being located on opposite sides of said workpiece andmovable toward and away from said workpiece; e) means for moving saidframe in a first direction along said supporting surface and along saidworkpiece; f) means for moving said carriage means in a directionsubstantially perpendicular to said first direction and toward and awayfrom said supporting surface; g) means including said converting meansfor moving said riveting tools toward and away from said workpiece; h)means operatively associated with said positioning means for moving saidfirst and second head means about an axis substantially parallel to saidfirst direction and to said supporting surface; and i) means operativelyassociated with said positioning means for moving said first and secondhead means about an axis substantially perpendicular to said firstdirection and to said supporting surface.
 29. Method of riveting two ormore side-by-side workpieces together, the workpieces being providedwith aligned apertures in which a slug rivet has been received, one sideof one workpiece establishing a substantially fixed work plane; saidmethod comprising the following steps: providing first and secondriveting rams means aligned with the slug rivet, the first riveting rammeans being disposed adjacent said one side of said one workpiece, andthe second riveting ram being disposed away from the outer side ofanother workpiece; moving the first riveting ram means with respect tothe work plane to establish a first desired die cavity; moving thesecond riveting ram means towards the first riveting ram means untilboth ends of the slug rivet are just in contact with both riveting ramsmeans; simultaneously moving the first and second riveting ram meanstowards each other at equal rates to simultaneously form upset heads onboth ends of the slug rivet while said one side of the one workpiececontinues to be disposed in the work plane; and said steps of moving thefirst riveting ram means, moving the second riveting ram means andsimultaneously moving the first and second riveting ram means beingperformed utilizing the method of claim 20 or claim 22 .
 30. A methodfor riveting two or more side-by-side workpieces together with opposedupper and lower riveting ram assemblies, the workpieces being providedwith aligned apertures in which a slug rivet has been inserted;comprising the following steps: positioning the upper riveting ramassembly against an upward movement limiting stop to establish an upperdie cavity; applying an upward force to move the lower riveting ramassembly upwardly towards the upper riveting ram assembly until bothends of the slug rivet are snugly engaged between adjacent ends of theupper and the lower riveting ram assemblies; applying a downward forceto the upper riveting ram assembly after both ends of the slug rivet aresnugly engaged until the downward force of the upper riveting ramassembly equals the upward force applied to the lower riveting ramassembly, without any deformation of the rivet occurring due to theequal forces; and then; simultaneously moving the upper and lower ramassemblies towards each other to simultaneously form upset heads on bothends of the river, thereby compensating for deflection of a framecarrying said upper and lower ram assemblies; said steps of applying anupward force, applying a downward force and simultaneously moving theupper and lower ram assemblies towards each other being performedutilizing the method of claim 20 or claim 22 .